It is known that the installation of a staircase in a building introduces a certain number of constraints. So as to determine the dimensional characteristics of a staircase, one skilled in the art must take account of the available space and observe the customary dimensional relation between the height of the riser and the width of the tread. For this reason it is difficult to standardize the dimensions of a staircase and this latter may not be prefabricated in series.
So as to construct staircase, it is desirable to take account of the actual dimensions of the staircase housing, and not those initially provided by the architect. In effect, taking account of the dimensional tolerances allowed in the profession, the actual dimensions of the staircase housing may differ some centimeters from those initially provided. These dimensional deviations are conventionally compensated for on the dimensions of the steps of the staircase.
So as to reduce the cost of manufacture of staircases, these latter are realized in molded concrete. In the field of this technique, adjustable molds are conventionally used which permit realizing staircases of different dimensions, that is to say staircases having differing dimensions of extent, riser height and tread width.
Such molds generally comprise a series of elements for molding steps each constituted by a first metallic wall intended to form the tread and by a second metallic wall intended to form the riser.
These two walls are rigidly fixed the one to the other and are perpendicular the one to the other. The molding elements are mounted on a frame in a mutual covering so as to form a succession of triangular cavities and projections.
So as to adjust the dimensions of the tread and the riser these molding elements may be displaced the ones with respect to the others.
Thus for adjusting the width of the treads, each molding element is displaced so as to cover more or less the adjacent molding element whereas for adjusting the height of the risers each molding element is spaced more or less from the adjacent molding element. Each molding element bears on the adjacent molding element, with interposition of wedges.
The principal inconvenience of this type of molding resides in the fact that this latter is largely unsealed. There then results at the time of molding losses of laitance. This laitance flows out on the adjusting mechanisms for the positioning of the molding elements. Upon drying, the laitance blocks this mechanism. Because of this inconvenience, one skilled in the art, after each molding, must proceed to the cleaning of the mold. This long and onerous operation consequently encumbers the cost of use. Moreover, the loss of laitance is manifested in the obtention of molded elements having a rough or grainy appearance.
Another inconvenience of this type of molding resides in the fact that it is impossible to mold staircases of which the treads form an acute angle with the risers, so as to form a curved interval.